Abstract

The apparently single, rapidly rotating G giant FK Comae displays an
unusual hydrogen alpha emission line which is very broad, strong, and
variable. Extensive high-resolution studies of this line with complete
phase coverage are presented. The alpha hydrogen emission centroid shows
a radial velocity modulation on the 2.4 days stellar rotation period
with a semiamplitude identical to the photospheric rotational velocity.
These data, when phased with optical photometry, indicate that the star
has a bright, rather than dark, region on its surface and that the phase
may have been stable for seven years. A qualitative model wherein the
bright spot is caused by accretion from a low mass unseen companion onto
the surface of the G giant is considered. Such a model explains many of
the observed characteristics of the stellar spectrum and hydrogen alpha
feature, and it is concluded that FK Comae is not yet a single star, but
is still evolving toward coalescence of the system.

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